This invention relates to the recording of data on a high speed moving recording media which is subject to stoppage, such as a tape, and, more particularly, to the correlation of data processing data sets to the media position and resynchronizing the media position to the data set sequence upon restart of the media movement.
Typically, longitudinal media, such as magnetic tape or optical tape, is employed in data processing systems as a secondary storage media for storing large amounts of data for low cost, infrequently used data or for archival purposes. Often, the data (in the form of a series of data sets) is transferred to the longitudinal media for writing on the media by streaming. Similarly, the data is often read on a continuous basis. The data transfer is, however, subject to interruption or to a temporary fault condition while the media continues to move at its continuous nominal velocity. Thus, the media must be stopped, and later restarted.
On restart, the media position must be correlated and resynchronized with respect to the data set sequence. A typical prior art tape drive which moves the tape media is equipped with an incremental encoder, or tachometer, which provides a precise positioning signal to counters which monitor media position. The tape drive may then reposition the tape media backwards, also known as a back hitch, a certain amount based on the incremental encoder positioning signal and restart the tape so that the tape is up to speed by the time it reaches the point at which the data transfer ended. If the tape did not slip, the incremental encoder or tachometer, and counters should identify the point at which the data transfer ended, and the data transfer is resumed.
Cost reduction is of key importance in modern tape drives and other longitudinal media drives. Precision incremental encoders are expensive and it is desirable to provide an alternative, which may allow the elimination of the incremental encoder.
Special indexing or clocking tracks have been employed, but modern data processing tape drives maximize the number of data tracks on the tape media. Thus, elimination of any non-data special indexing or clocking tracks is essential.
An object of the present invention is to identify the point at which the data transfer ended, and resume the data transfer without requiring an incremental encoder.
Disclosed are system and method for precisely registering and synchronizing data sets on a recording media, the recording media having a prerecorded servo pattern. The drive has a servo system for reading the prerecorded servo pattern on the recording media. The recording media is subject to continuing movement for reading and/or writing the data sets, interrupted by stopping at the end of a selected data set and restarting.
In the present method, during the continuing movement of the recording media while reading and/or writing data sets on the recording media, a detector coupled to the servo system continuously reads linear position registration data modulated or superimposed in the prerecorded servo pattern on the recording media. An interpolator interpolates the prerecorded linear position registration data to provide precision registration information for the data sets. Upon the stopping of the recording media, the recording media is back hitched in the opposite direction, and the movement is restarted by the drive. Upon the back hitch and restart, selected read and interpolated registration information is provided. The detector again reads and interpolates the prerecorded registration data (defined as the xe2x80x9cagain read data and interpolatedxe2x80x9d data), and a comparator compares the again read and interpolated registration information to the provided read and interpolated registration information, and indicates a comparison match. A data formatter coupled to the comparator, responsive to the comparison match indication, synchronizes the reading and/or writing data sets on the recording media.
In another aspect of the present invention, a magnetic tape media having prerecorded interpolatable linear position registration data information recorded in magnetic flux transition servo patterns defining at least one longitudinal servo track is provided with a plurality of frames of alternating groups of burst patterns. Each group of burst patterns has alternating numbers of at least two repeated pairs of non-parallel magnetic flux track following servo transitions. At least two of the transitions of the repeated pairs are shifted longitudinally with respect to other of the transitions of the repeated pairs. The shifted transitions comprise registration data information, and each frame or group comprises interpolation information.
An advantage of the present invention is that the registration information is provided directly on the media, so that no reliance is placed on preventing slip between the media and the incremental encoder.
For a fuller understanding of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.